Typical coaxial cable includes one or more layers of radio frequency (RF) shielding. One common type of shielding is a conductive tape that attenuates interfering electromagnetic fields in the high frequency range. Another common type of shielding is a conductive braid that attenuates interfering electromagnetic fields in the low frequency range. For example, a typical tri-shield coaxial cable includes a center conductor surrounded by a dielectric, an inner tape, a braid, an outer tape, and a jacket.
Prior to the manufacture of a tri-shield coaxial cable, the inner and outer tapes are each shaped as a flat ribbon. During the manufacture of the cable, the inner tape is folded around the dielectric such that the two edges of the inner tape overlap one another to form a straight seam that runs the length of the cable. The braid is next formed around the inner tape, after which the outer tape is folded around the braid such that the two edges of the outer tape overlap one another to form another straight seam that runs the length of the cable. Finally, the jacket is extruded around the outer tape.
After manufacture and prior to use of the tri-shield coaxial cable, the ends of the cable must be terminated with cable connectors. Prior to termination with a cable connector, a quarter-inch section of the center conductor must be exposed by removing all other layers. In addition, immediately adjacent to the quarter-inch section of the exposed center conductor, a quarter-inch section of the jacket and the outer tape must also be removed, thereby exposing a quarter-inch section of the braid. The braid is then folded back over the jacket so that a circular post (or similar structure) of a cable connector can be inserted between the inner tape and the braid.
Some tri-shield coaxial cables are manufactured such that substantially all of the outer surface of the outer tape is bonded to the inner surface of the jacket. One advantage of this bonding is that the quarter-inch section of outer tape can be removed simultaneously with the quarter-inch section of jacket after the jacket is circumscribed with the cutting edge of a cable preparation tool. One drawback of this bonding, however, is that any flexure of the jacket while the coaxial cable is in service causes a corresponding flexure of the outer tape. This flexure of the outer tape causes micro-cracks to develop in the tape which degrades the shielding effectiveness of the tape. Another drawback is that contact with the aluminum in the outer tape tends to wear down the cutting edge of the cable preparation tool.
Other tri-shield cables are manufactured such that the outer tape is not bonded to the jacket. One advantage of not bonding the outer tape to the jacket is that the outer tape can move independently of the jacket during flexure of the jacket, thus decreasing micro-crack degradation of the outer tape. One drawback with not bonding these two layers, however, is that this independent movement of the outer tape tends to cause the two overlapping edges of the outer tape seam to separate during flexure of the jacket. This separation degrades the shielding effectiveness of the outer tape.